Deposition reactor

ABSTRACT

A reactor for depositing a thin layer of material on a semiconductor slice by thermal decomposition of reactant gases is disclosed which has a circular rail, a number of disk-shaped graphite susceptors or supports each having a flat face from which projects a circular retaining rim, a member rotating on an axis extending through the circular rail for rolling the susceptors along the rail while supporting the susceptors at an inclined angle, and an RF coil for heating the susceptors as they are rolled along the rail. The edge of a semiconductor slice placed on the face of the susceptor rolls around the rim of the susceptor as the susceptor rolls. This mechanism is enclosed in a chamber and the reactant gases passed through the chamber. Thus, anomalies in the RF field are compensated as the susceptor rolls around the rail to evenly heat the susceptor, thermal anomalies in the susceptors are compensated as the slice continually moves over the susceptor, and anomalies in the composition of the reactant stream are compensated as each semiconductor slice rotates about its own axis while being translated in a circular path through the vapor stream. Layers uniform in thickness within + OR - 0.5 percent have been achieved, representing an order of magnitude improvement over prior art devices, with corresponding improvements in the uniformity of doping levels and resistivities.

United States Patent [72] Inventors Kenneth E. Bean Richardson; John R. Camplon, Garland, both 01 Tex. [2]] Appl. No. 788,250 [22] Filed Dec.3l, 1968 [45] Patented Sept. 28,1971 [73] Assignee Texas Instruments Incorporated Dallas, Tex.

[54] DEPOSITION REACTOR 6 Claims, 4 Drawing Figs.

[52] U.S.Cl 118/48, 1 118/500 [51] Int. Cl B05c11/14 [50] Field of Search ..l 18/49-495, 500, 503; 148/74, 75; 117/106-1072 [56] References Cited UNITED STATES PATENTS 3,523,517 8/1970 Corbani 118/500 2,260,471 10/1941 McLeod 118/49 2,532,971 12/1950 Van Leer etal. 1l8/49.1 X 2,997,979 8/1961 Tassara 118/49 3,128,205 4/1964 lllsley 118/49 3,205,087 9/1965 Allen... 118/49.1 X 3,408,982 l [/1968 Capita..... 118/49.5 3,424,629 1/1969 Ernst et al... 118/48 3,442,572 5/1969 Illsley et al.. .1 11.8/49 X 3,486,237 12/1969 Sawicki 118/500 X Primary Examiner-Morris Kaplan Attorneys-James 0. Dixon, Andrew M. Hassell, Melvin Sharp, Harold Levine, John E. Vandigriff, Henry T. Olsen and Michael A. Sileo, Jr.

ABSTRACT: A reactor for depositing a thin layer of material on a semiconductor slice by thermal decomposition of reactant gases is disclosed which has a circular rail, a number of disk-shaped graphite susceptors or supports each having a flat face from which projects a circular retaining rim, a member rotating on an axis extending through the circular rail for rolling the susceptors along the rail while supporting the susceptors at an inclined angle, and an RF coil for heating the susceptors as they are rolled along the rail. The edge of a semiconductor slice placed on the face of the susceptor rolls around the rim of the susceptor as the susceptor rolls. This mechanism is enclosed in a chamber and the reactant gases passed through the chamber. Thus, anomalies in the RF field are compensated as the susceptor rolls around the rail to evenly heat the susceptor, thermal anomalies in the susceptors are compensated as the slice continually moves over the susceptor, and anomalies in the composition of the reactant stream are compensated as each semiconductor slice rotates about its own axis while being translated in a circular path through the vapor stream. Layers uniform in thickness within 10.5 percent have been achieved, representing an order of magnitude improvement over prior art devices, with corresponding improvements in the uniformity of doping levels and resistivities.

mw'rensmemn 3,608,519

sum 1 or 2 INVENTOH:

KENNETH E. BEAN JOHN R. CAMPION PMENTED SEPZBIBII 3,608.51 9

SHEET 2 [1F 2 mvemons KENNETH E. BEAN JOHN R. CAMPION DEPOSITION REACTOR This invention relates to apparatus for heating an article to a uniform average temperature over its surface, and for subjecting such article to a fluid stream of uniform average composition over the surface of the article, and more particularly, but not by way of limitation, relates to the deposition of very uniform layers on a semiconductor slice by thermal decomposition of certain reactant gases.

Reactors heretofore utilized to chemically deposit epitaxial films, polycrystalline films, dielectric films, and the like in the manufacture of semiconductor devices have been unable to deposit films uniform in thickness within less than percent across a l.25-inch diameter slice. Epitaxial films deposited by the prior art reactors have even greater resistivity gradients as the result of variations in substrate temperature causing variations in doping level of the film across the slice. The more advanced reactors for carrying out these processes place the semiconductor slices on a horizontal surface of a susceptor which is then translated relative to both the RF field and the reactant stream.

This invention is concerned with an improved reactor in which the semiconductor slices or substrates are heated to a very uniform average temperature over the entire slice, and the slice is subjected to a very uniform average reactant stream over the entire slice. This is achieved by translating the slice over the surface of the susceptor or support used to heat the slice, while simultaneously translating the slice through the reactant stream. More specifically, the slice is both translated in a circular path and rotated about its own axis relative to both the reactant stream and the susceptor. .The susceptor is also rotated about its axis and translated relative to an RF field to achieve uniform heating of the susceptor.

The invention is claimed as an apparatus in various combinations and subcombinations. As specifically claimed, the invention has the additional advantages of positioning the slices at an angle. This feature reduces contamination by solid particles coming to rest on the slice, reduces the requirement that the reactant stream have uniform composition in the reactant zone, and permits a substantially smaller vacuum chamber than previous devices to be used to process the same number of slices of the same size. The reduction in the size of the vacuum chamber materially reduces the volume of reactant gases required, and therefore the purge cycle times. ln addition, the specific apparatus claimed materially reduces the latent heat stored in the system during a process cycle, thus materially reducing the start up and cool down times required. Thus, in addition to producing films of superior quality, the reactor also has a greater production rate, is less expensive to operate, is able to accommodate more slices per given volume of reactant gases and consequently is safer and more efficient and requires less capital investment.

The novel features believed characteristic of this invention are set forth in the appended claims. The invention itself, however, as well as other objects and advantages thereof, may best be understood by reference to the following detailed descrip' tion of illustrative embodiments, when read in conjunction with the accompanying drawings, wherein:

FIG. 1 is a perspective view of a reactor constructed in accordance with the present invention;

FlG. 2 is a partial vertical sectional view of the reactor of FIG. 1;

FIG. 3 is an enlarged sectional view of a portion of the reactor of FIG. 1; and

HO. 4 is a somewhat schematic plan view of another reactor in accordance with the present invention.

Referring now to the drawings, a reactor constructed in ac cordance with the present invention is indicated generally by the reference numeral 10. The reactor is comprised of a transparent bell jar 12 which rests on the top surface 14 of a base 16 to form a chamber. The base 16 includes a number of conventional items which are not illustrated, including a system for evacuating or pressurizing the bell jar 12, and a system for selectively introducing one or more gas streams into the reactor, and plumbing for circulating a cooling fluid through the base. The system also includes a conventional system for rotating a tubular shaft 24, which extends into the chamber, while passing a reactant gas stream through the shaft into the vacuum chamber. The portion of the system described to this point is of conventional design.

ln accordance with the present invention, a quartz cylinder 18 forms a circular rail 20 at the upper end. A drive mechanism, indicated generally by the reference numeral 22, is comprised of the tubular shaft 24 which is flared at the upper end to form a depending spherically shaped dome 26, the shaft and dome being an integral body of quartz. The shaft 24 is rotated by a suitable motor disposed within the base 16 and coupled to the shaft by a suitable conventional mechanical feedthrough system. Such a drive system may employ either a direct or a magnetic coupling. In addition, the lower end of the tubular shaft 24 is in fluid communication with a source of reactant gas located outside the chamber formed by the bell jar 12 and the base 16 by a conventional rotary coupling also located in the base 16.

A plurality of quartz push rods 30 extend downwardly and outwardly from rim 28 of the dome 26.

Six graphite, disk-shaped susceptors, indicated generally by the reference numerals 32-37, are rolled around the circular track 20 by the drive mechanism 22. Each of the susceptors is constructed substantially as illustrated in FIG. 3 wherein susceptor 33 is specifically illustrated. The susceptor 33, chosen randomly for illustration, has a disk-shaped main body 40 with a cylindrical extension 42 which terminates in an annular flange 44 to form an outwardly facing annular groove 46. The annular groove 46 rolls on the rail 20 formed by upper edge of the cylinder 18, and the rear face 48 of the body 40 slides on the outer face of the edge 28 of the spherical portion 26 of the drive mechanism 22. The ends of the push rods 30 extend into the groove 46 to engage the cylindrical extension 42 and thus roll the susceptor 33 around the circular rail 20 as the shaft 24 is rotated.

The front face 50 of the susceptor 33 is provided with three indentations each having a recessed flat face 52 and a cylindrical sidewall which forms a rim 54 upon which the edge of a semiconductor slice 56 rolls as it slides over the face 52. The diameters of the rims 54 are larger than the diameters of the semiconductor slices 56 and are preferably chosen so that any given point on a slice 56 does not trace the same path on the surface 52 during successive revolutions of the susceptor. The susceptors may have a single large recess as illustrated on the face of susceptor 34 to receive a larger semiconductor slice 58, or to receive a slice 56.

The graphite susceptors 32-37 are heated by a water cooled RF coil 62 which is frustoconically shaped and positioned so as to bridge the annular space between the circular rail 20 and the lower edge of the spherical section 26 of the drive means. The RF coil 62 is formed of metal tubing through which cool water is circulated. It should be noted that the RF field induces currents only in the graphite susceptors, since all other structures in the RF field, including the cylinder 18 and the quartz drive assembly 22 are nonconductive. Within the broader aspects of the invention, the susceptors could be heated electrically either directly or by radiation from a resistive element.

As previously mentioned, the chamber formed by the bell jar 12 and base 16 may be evacuated or pressurized by conventional means. Reactant gases may be introduced through the tubular shaft 24. In addition, a plurality of diffusers 60 are located in relatively close position to the faces of the semiconductor slices carried by the susceptors, and preferably slightly above, so that gases introduced through the diffusers will mix with the gases introduced through the shaft 24 immediately prior to passing through the reactant zone through which the susceptors pass. These reactant gases are, of course, withdrawn from the chamber through a suitable conventional evacuation outlet which is not illustrated.

The reactor may be used for depositing a variety of films, and particularly can be used for depositing substantially all layers used in the fabrication of semiconductor devices. For example, silicon dioxide coatings may be deposited by introducing silane through the drive shaft 24 and oxygen through the diffusers 60 while maintaining the semiconductor slices at a temperature in the range from about 200 C. to about 500 C. A silicon nitride passivating layer may be deposited at temperatures from about 550 C. to about l,200 C. using silane and ammonia. Various silicon epitaxial depositions can be carried out at temperatures ranging from about 900 C. to about 1,250 C. using various reactant gases. These processes may or may not be carried out at subatmospheric pressures. Moreover, the reactor according to the invention may be utilized for vapor etching of the substrate surface. In the operation of the reactor 10, the susceptors 32-37 may be loaded with the semiconductor slices inside or outside the reactor. The susceptors are positioned on the edge of cylinder 18 with the upper edge slidably resting on the edge of the spherical portion 26 of the drive means. The bell jar 12 may then be placed in position on the base 16 and the chamber evacuated or purged as required. The shaft 24 is set in motion so that the push rods 30 depending from the dome 26 propel the susceptors 32-37 around the circular rail 20. The susceptors roll along the rail 20 with the rear face 48 sliding on the edge of the dome 26. As the susceptors rotate, the edges of the semiconductor slices 56 and 58 roll on the rims 54 of the depressions. Since the rims 54 have a greater diameter than that of the semiconductor slices, the slices also slide over the recessed faces 52. The circumferences of the rims 54 are greater than the circumferences of the slices 56, for example, and are preferably selected so as not to be an exact multiple of the circumference of the slice. As a result, each slice is continually rotated about its own axis while being simultaneously translated along a circular path over the face of the supporting susceptor as the susceptor is rolled around the track 20, and each point on the slice continually passes over a different portion of the susceptor, thus compensating for any thermal anomalies in the susceptor resulting from anomalies in the resistance of the graphite susceptors, or in hysteresis effects due to spacing, etc. The respective diameters of the slice and recess may be chosen to effect the desired relative rotational frequency of the slice and support about their own axes.

The circumference of the groove 46 in the susceptors is selected with relationship to the circumference of the rail 20 so that each point on the susceptor traces a sinusoidal path that is continuously shifting in position relative to the RF field, thus compensating for anomalies in the RF field by averaging.

Any anomalies in the reactor gas field are similarly compensated as the slices are both rotated about their own axis and translated in a circular path through the reactant field. In addition, when the rim upon which the semiconductor slice rolls is eccentric to the axis of the susceptor, as in the case of rim 54 on susceptor 33, the semiconductor slice is translated through an upright cycloptical or sinusoidal path. Of course, the rims defining the depressions can be of any desired shape to cause the semiconductor slices to move up and down as they traverse the circular path. In addition, the shaft 24 can be slightly eccentric with respect to the cylinder 18 so that the angle of the susceptors to the vertical can be alternately increased and decreased as the susceptors transverse the circular path. Or the track 20 may be irregular to achieve a desired motion of the susceptors.

As a result of using the reactor 10, coatings have been deposited which are uniform in thickness within :5 percent, representing an order of magnitude improvement over prior techniques wherein thicknesses could be controlled within only :5 percent. A commensurate improvement in uniformity of resistivity and other electrical characteristics is also obtained.

Other important advantages are obtained -by placing the.

particles in the gas stream to come to rest upon the surface of the semiconductor slices. This tendency is further reduced by reason of the fact that the slices are continually in motion and subjected to some slight vibration. Or a separate vibrating means may be combined with the system to effect the desired vibration. Further, by placing the susceptors on edge, a greater number of large susceptors can be placed in a bell jar of the same diameter, and thus of the same volume. For example, only about 25 percent of the volume of gas is required for the reactor 10 as compared with prior art reactors required for the reactor 10 as compared with prior art reactors required to process the same number of the same size slices. The smaller volume also requires shorter purging and outgassing times at the beginning and end of the process period, thus reducing the overall turn around time between successive runs. Since the slices are continually in motion, thick layers, such as epitaxial layers, do not tend to cause the slices to stick to the susceptors, as is the case when the slices rest in the same position on the susceptor throughout the deposition process. Another technique for achieving relative movement between the slices and susceptor would be to rotate an inclined susceptor about its center thereby causing the slices to rotate within the recesses.

Referring now to FIG. 4, another reactor in accordance with the present invention is indicated generally by the reference numeral 70. The device 70 illustrates that the basic principles of reactor 10 are particularly adapted to a continuous process system. in reactor 70, the susceptors 72 are brought into the reactor chamber 74 along rail 76, rolled around rail 78 by drive mechanism 84, and then taken from the chamber along rail 80. A suitable mechanism (not illustrated) may be provided to load and unload the susceptors on the circular rail 78 from the rails 76 and 80. The reactant gases may again be introduced through the vertical hollow shaft 82 of the drive mechanism 84, and the diffusers 86. The continuous flow process is particularly useful when the deposition process is carried out in a controlled environment at atmospheric pressure, in which case the reactant gases are kept at a slightly higher pressure than atmospheric to prevent the inflow of atmospheric gases into the chamber through the passageways used into and out of the chamber for the susceptors. The path of the susceptors can also can be straight through a tunnel, moving against the flow of reactant gases, for example.

lt is to be noted that one advantage of the invention is that the layer deposited on a slice will not bond the slice to the support due to the relative motion between the slice and support. Another technique may be utilized with the present invention for heating the substrate which is to initially raise the temperature of the substrate above its curie point in order to render it conductive by, for example, resistance heating or are image heating and then after it is rendered conductive RF induction heating may be utilized. By this technique, nonconductive supports could be utilized and such supports would not be materially heated since only the substrate is heated.

Although preferred embodiments of the invention have been described in detail, it is to be understood that various changes, substitutions and alterations can be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

what is claimed is:

1. In a system for depositing a uniform layer of material on a substrate, the combination of:

means for supporting a plurality of disk-shaped susceptors at an oblique angle,

said susceptors each including, in the outer face thereof, at

least one circular recessed portion having a closed bot tom,

a disk-shaped substrate of smaller: diameter than said recess supported within each of said recessed portions, means for heating said substrates on the susceptors, means for passing a reactant. gas stream over said substrates,

means for rotating and simultaneously orbiting said susceptors relative to said support whereby to effect rolling movement of each said substrate relative to the rim which defines the recessed portion associated therewith.

2. The combination of claim 1 wherein the reactant gas stream is made to flow downwardly over the substrates.

3. A vapor deposition coating system comprising in combination:

a coating chamber;

a plurality of disk-shaped support members within said chamber, each having a continuous rim on the outer face thereof to define a closed-bottom recess for holding a substrate to be coated;

a disk-shaped substrate of a lesser diameter than, and supported within, the circular recess defined by each said rim;

means for rotating each of said support members at an inclined angle;

means for orbiting said support members about a generally central point within said chamber and simultaneously with rotation induced by said means for rotating whereby to effect rolling movement of each said substrate relative to the rim associated therewith;

means for heating said support members; and

means for passing a reactive gas stream over and in contact with the substrates supported thereon.

4. A system as defined by claim 3 further including means for loading and unloading said support members into and from said chamber.

5. A system as defined by claim 3 wherein at least one of said support members has a plurality of recessed surfaces for holding a plurality of substrates.

6. A system as defined by claim 3 wherein said support members are graphite susceptors and said heating means comprises an RF coil. 

2. The combination of claim 1 wherein the reactant gas stream is made to flow downwardly over the substrates.
 3. A vapor deposition coating system comprising in combination: a coating chamber; a plurality of disk-shaped support members within said chamber, each having a continuous rim on the outer face thereof to define a closed-bottom recess for holding a substrate to be coated; a disk-shaped substrate of a lesser diameter than, and supported within, the circular recess deFined by each said rim; means for rotating each of said support members at an inclined angle; means for orbiting said support members about a generally central point within said chamber and simultaneously with rotation induced by said means for rotating whereby to effect rolling movement of each said substrate relative to the rim associated therewith; means for heating said support members; and means for passing a reactive gas stream over and in contact with the substrates supported thereon.
 4. A system as defined by claim 3 further including means for loading and unloading said support members into and from said chamber.
 5. A system as defined by claim 3 wherein at least one of said support members has a plurality of recessed surfaces for holding a plurality of substrates.
 6. A system as defined by claim 3 wherein said support members are graphite susceptors and said heating means comprises an RF coil. 